Electric blanket control



May 30, 1950 A. E. RUDAHL ELECTRIC BLANKET CONTROL Filed April 22, 1948ARA/OLD E PUD/4H4 Patented May 30, 1950 UNITED STATES PATENT OFFICEELECTRIC BLANKET CONTROL Arnold E. Rudahl, Middlefield, Conn, assignorto Landers, Frary & Clark, New Britain, Conn., a corporation ofConnecticut Application April 22, 1948, Serial No. 22,570

(Cl. 2l920) 11 Claims. 1

The present invention relates to electric blankets of the type having anelectric heating unit arranged in a blanket fabric and is moreparticularly directed to an improved arrangement for controlling theapplication of electrical energy to the heating unit so as to insure thecomplete safety and comfort of the user.

It is an object of the invention to provide a control arrangement for anelectric blanket which is extremely sensitive in operation such that theamount of heat generated within the blanket can be precisely establishedand controlled.

Another objeot of the invention is to provide a control arrangementwhich is responsive to blanket temperature or ambient temperature, orpreferably to both, so that the amount of heat required for the comfortof the user can be automatically determined under varying conditions ofuse and so that any incipient fire hazard will be immediately detectedand avoided.

A further object of the invention is to provide a control arrangementincluding a motor timer, preferably an electrically driven timer, suchthat the thermally operated switches and relays commonly used inelectric blanket controls with their attendant inaccuracies, slowoperation and noisy functioning are eliminated and such that there maybe incorporated into the controls as part of the timer a bedside clockto indicate time and with provision for automatic opening of the heatingcircuit at a predetermined selected time as desired.

Another object of the invention is to provide a control means in whichthe electric heating unit itself may be utilized as an instrumentalityin the blanket which is utilized for rendering the control responsive totemperatures within the blanket.

Another object of the invention is to provide a control arrangementwhich is simple and economical to. fabricate and assemble from standardparts and which is so constructed that it will not readily get out oforder or require adjustment or replacement over long periods of time.

Other objects will be in part obvious and in part pointed out more indetail hereinafter.

The invention accordingly consists in the features of construction,combination of elements and arrangement of parts which will beexemplifled in the construction hereafter set forth and the scope of theapplication of which will be indicated in the appended claims.

In the drawing, the single figure is a diagram- 2 matic view of oneembodiment of the control arrangement of the present invention.

Referring to the drawing, the main elements of the arrangement shown arethe electric blanket A, a resistor B which is subjected to ambienttemperatures, an adjustable reference resistor C, a transformer D, anelectronic tube E, a selflocking relay F and a timer G. In theembodiment shown, the control circuit, the timer G and the electricblanket A are energized by connection to the lines LI and L2 of aconventional household lighting system.

The electric blanket A may be of conventional construction and thereforeis shown merely diagrammatically. The heating element l0 may be aresistance wire of any suitable metal or alloy and preferably isdisposed throughout the blanket in a plurality of convolutions. In thepreferred embodiment, the heater wire metal or alloy selected is onewhich has a resistance which varies proportionately with itstemperature. A copper wire, for example, would have suchcharacteristics. For the purposes of the present disclosure, it will beassumed that the temperature co-efiicient of resistance of the heatingelement [0 is strongly positive, 1. e., its resistance appreciablyincreases in relationship to increases in its temperature.

The resistor B similarly is composed of a metal or alloy which has aresistance responsive to its temperature changes and, as in the case ofthe heating element It, it will be assumed that the temperatureco-eflicient of resistance of the resistor B is positive. The resistor Bmay be a suitable length of copper wire, for example, wound in the formof a grid. The resistor 13 is intended to be located where it will besubjected to ambient temperatures, that is, so that in normal usage ofthe blanket it will be subjected to the same temperature as that of theair in the room. In general, this desired location of the resistor 13may be accomplished by placing the same in the bedside control boxprovided the latter is suitably ventilated.

The reference resistor C is constructed of a material having asubstantially constant resistance at varying temperatures, i. e., asubstantially zero or very small temperature co-efiicient of resistance.As a result, the reference resistor C, when suitably adjusted to providea desired resistance, will remain a substantially constant factorregardless of the temperature conditions to which it is subjected.

The transformer D includes a primary l5 having terminals I1 and I8 andbeing provided with taps l6, I9 and 29. The secondary 2! of thetransformer D is utilized to provide the heating current for thefilament 29 of the electronic tube E or other tubes utilized in thecontrol system.

The primary l5 of the transformer D, the reference resistor C, theambient temperature responsive resistor B and the blanket heatingelement It are arranged to be connected in the form of a bridge circuit.One leg of the bridge circuit comprises the resistor B and the heatingelement I6; a second leg of the bridge circuit includes the portion ofthe primary I5 extending between tap l9 and terminal ll; a third leg ofthe bridge includes the portion of the primary 55 extending between tapsi8 and i9, and the fourth leg of the bridge comprises the referenceresistor C. Terminals and 26 of the reference resistor C and the ambienttemperature responsive resistor B, respectively, are connected to a,normally open switch 27 and when this switch '21 is closed the bridgecircuit is completed. The values of the resistors C and B and thelocation of the taps i8 and i9 are selected so that the bridge is inbalance when the. resistance B and the heater element it are at apredetermined temperature such as room 3 temperature. In general, it isdesirable to select a resistance value for resistor C which issubstantially equal to the sum of the resistances of resistorB andheater unit it]. The resistance value Of resistor B is. selected inaccordance with the desired proportionate sensitivity of the circuit toambient and blanket temperatures. The greater the resistance of B, thegreater will be the relative effect or" changes in ambient temperaturesas compared with blanket temperatures;

The terminal N5 of the transformer D is connected to the plate 30 of theelectronic tube E through the normally closed switch 23 and the solenoidwinding 10, switch arm M and terminal 42 of the relay F. When thesolenoid winding is not energized, the switch arm 4! is in the positionshown in the drawing. However, when the solenoid winding 49 isenergized, the switch arm 4! is moved to an upper position at which itcomes into contact with terminal 63.

The terminal 25 of the bridge circuit is connected to the cathode 3! ofthe electronic tube E. Accordingly, when the switch 21 is in the openposition shown in the drawing, there is only a very small plate voltageimpressed on the electronic tube E, namely, that generated between tapl8 and terminal it of the transformer primary winding l5. When theswitch 27! is closed, however, the bridge circuit is put into operationthereupon placing the cathode ti under voltage which, when the resistorC is substantially equal tothe sum of resistor B and heating unit it, isapproximately half of the line voltage plus the additional voltageinduced in the segment of the primary between terminal l6 and tap H3.The additional voltage supplied by the portion of the primary betweenterminal 15 and tap i8 is desired particularly when the electronic tubeE is a thyratron which requires an operating voltage higher than half ofthe line voltage.

The flow of current through the electronic tube E is controlled by thegrid bias on the control grid 32. The control grid 32. is connectedthrough, resistor 34 to a potentiometer 35 which is connected acrosstaps i9 nd 2t. Inasmuch as the terminal 25 of the bridge circuit isconnected to the cathode 3|, it will be seen that the grid bias will beequal to the voltage unbalance of the bridge circuit plus a voltageincrement developed in the potentiometer 35. If desired, thepotentiometer 35 may be situated that it may be manipulated by the useras a control member for predetermining the amount of heat which will begenerated in the blanket for a given set of temera are conditions tosuit his comfort. This result obtains because the setting ofpotentiometer it determines the amount of unbalance of the bridge whichwill be required to cause the electronic tube E to discharge and theamount of unbalance is function of the temperature of resistor B andheating element [0.

Inasmuch as the circuit is operated on alternating current, the resistor3 is employed to prevent grid current during the reverse cycle. Thescreen grid 33 in this instance is connected directly to the cathode 3|.

As will be noted in the drawing, the line L2 of the household supplycircuit is directly connected to one side of the heating element I!)while terminal intermediate resistor B and heating waitv lii,'may beconnected through terminal 44 and switch arm 45 of the relay F to thetap i8 transformer D which, in turn, is connected by a circuit to bedescribed hereinafter to the line of the household lighting circuit.When the solenoid winding 4!] is energized, the switch s5 is drawndownwardly to make contact the terminal 44 thus connecting the heaterdirectly across the lines Ll, L22. lerminal E3 of the relay Fisconnected to the tap. id. of the transformer D so that when thesolenoid winding 49 is energized and the switch arm :ii is moved to anupward position making contact with terminal 43 the solenoid windingthis placed across tap l 9 and terminal 16 through switch 23 thuslocking the relay F in such energized position sov long as switch 28-remains closed.

It now will be observed that, in accordance with the invention, theclosing of switch. 2'5 will com-- plete the bridge circuit and if thereis a sufficient unbalance of the bridge as when the temperatureconditions in the blanket or ambient temperatures require the additionof heat through the heater unit. E792, then there will be a flow of 7current through the electronic tube E which energizes the solenoidwinding it causing the relay F to. loci; intov energized position, thusplacing the heating unit. it. across the line. The duration of theheating period may be interrupted at any time by opening theswitch 28.which deenergizes the solenoid winding it? permitting the relay F toreturn to the position shown in the drawing. By opening the switch 28and closing the switch 2'8 momentarily and in sequence at intervals, it

' is possible to make periodic measurements of the temperatureconditions both ambient and in the blanket and, if the temperatureconditions are such that heat isdesired, the blanket heating unit it maybe energized for the interval which the switch 28 remains closed. Themomentary and sequential operation of the switches 28 and 2'! isaccomplished in accordance; with the invention by the timer Gpreviously; referred to which may be any conventional clock mechanism orconstant speed, motor. In the specific embodiment shown in the drawing,an electric clock. motorgif utilized, may be connected by leads 5i and5! to lines LI and L2, respectively, A shaft 52 preferably driven by thesecond train of timer mechanism has mounted thereon a plurality of cams53 and 54 havingnibs 5E5 56 which are adapted to actuate the switches 23and 27. Upon each revolution of the shaft 52, the nib 54 of cam 54 willmomentarily open switch 28 following; which the nib 53 will momentarilyclose the switch 21. when shaft 52 is operated by the second train, itwill make a complete revolution every 60 seconds which is found toresult in a desired periodic operation of the switches 21 and 28.However, greater or lesser time intervals could be employed. By reasonof the above described mechanical operation of the switches 21 and 28,the control circuit is momentarily placed in a measuring condition for abrief period each minute, which period is of sufficient duration tocause the relay F to close and lock itself to the line if the blanket orambient temperature indicates that additional heat is required. Theclosing of relay F places the heater unit l6 into operation for theremainder of the period, approximately 50 seconds, until the switch 28is operated. On the next cycle, when the switch 2'! is closed, themeasuring function of the control circuit is repeated and if the blanketis still too cold the heating circuit is again energized. On the otherhand, if the blanket has acquired a sufficient amount of heat, therewill be no operation of the relay F and no heat will be applied to theblanket until a following cycle when the measuring circuit may detectthat further heat is required. It thus will be seen that the desiredamount of heat generated in the blanket A will be closely regulated asdesired by the user.

The operation of the switches 21 and 28 by the motor driven timer Ginsures that the operation of the bridge or measuring circuit will bedependable and only of very brief duration. Accordingly, it is possibleto use a heavy bridge current resulting in a large control signal whichwill make normal tube variations immaterial while at the same timekeeping the duration of such current to an unobjectionable minimum.Another feature of the arrangement is that in most cases, after theswitch 62 or 63 is first closed, there will be a time interval beforethe switches 21 and 28 will be actuated by the timer G, this becausesuch actuation occurs very briefly only once in each cycle. As a result,the tube E will normally have an opportunity to warm up before beingsubjected to a heavy plate voltage. This warm-up period plus the factthat the tube is conducting for only a minor fraction of the time thatthe blanket is in operation will tend to prolong the life of the tube ortubes utilized.

The circuit hereinbefore mentioned for connecting the tap [8 to the lineLl comprises a pair of leads 60 and 6| which are adapted to be connectedtogether either through switch 62 or switch 63.

The switch 63 is a snap action type switch and is constructed andarranged such that when it is moved to open or closed position it willremain in such position until again actuated. As shown diagrammaticallyin the drawing, the switch 63 is adapted to be closed by pressingdownwardly on the push button 64 and is adapted to be moved to the openposition by contact with a nib 65' on the cam 65 which preferably isdriven by the hour train of the timer and which preferably is adjustablein the same manner that the alarm is set on a conventional alarm clock.

In the embodiment shown in the drawing, the timer is provided with aconventional clock dial 66 and provided with time indicating hands 61and 68. An indicator 69 may be provided to show the setting of the cam65 and thus indicate at what time the switch 63 will be actuated to theopen position by the nib 65'. As will be apparent, the timer G may beprovided with an alarm mechanism, if desired, so that it may be utilizedas a bedside alarm clock and the ringing of the alarm .and the openingof the switch 63 may be arranged to occur simultaneously, although itwill be equally obvious that the operation of the alarm and the switch63 could be made to occur independently, if desired.

By virtue of the snap action switch 63 and the timer G, it is possiblefor the user to turn on the blanket upon retiring merely by pushing thepush button 64 and then the blanket will be turned ofi automatically atwhatever time is set by the indicator 69. On the other hand, if the userdesires to operate the blanket Without the automatic shut-off feature,he may close the circuit merely by closing the switch 62 which placesthe blanket and control circuit in operation independently of theoperation of switch 63, which operation will continue until the switch62 is again opened.

While the invention has been particularly described in connection withthe preferred specific embodiment shown in the drawing, it will beapparent that many variations in the circuits employed may be utilizedfor various reasons Without departing from the scope of the invention.For example, it will be apparent that either the resistor B or theheating element 10 may be eliminated from the bridge circuit, ifdesired, whereupon the control of the supply of electrical energy to theheating unit 16 would be responsive to ambient temperatures or blankettemperatures only. If the control circuit were responsive only toambient temperatures, however, additional means, such as thermostaticswitches in the blanket, might have to be employed to protect againstthe hazards of fire. Also, if desired, the instrumentality in theblanket for rendering the control circuit responsive to blankettemperatures may be a second resistor wire separate from the heatingunit l8 For simplicity of presentation, the electronic tube E has beenillustrated as a conventional thyratron. It will be readily apparent toone skilled in the art that other types of electronic tubes or a seriesof them could be substituted for the thyratron shown in the drawingwithout material departure from the teachin of the invention.

As many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language used in the followingclaims is intended to cover all of the generic and specific features ofthe invention herein described and all statements of the scope of theinvention which, as a matter of language, might be said to falltherebetween.

I claim as my invention:

1. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, an electric heating element insaid blanket whose resistance changes in relationship to changes in itstemperature, a resistance ele ment exterior to the blanket and subjectto ambient temperatures whose resistance changes in relationship to itstemperature, means including a normally open self-locking relay forapplying substantially full line voltage to said heating element from asource of electric power, a bridge circuit having one leg comprisingsaid heating element and said resistance element, means for periodicallyopening and closing said bridge circuit, means responsive to unbalanceof said bridge circuit when the bridge circuit is closed for energizingthe relay, and means for periodically unlocking said relay.

2. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, an electric heating element insaid blanket whose resistance changes in relationship to itstemperature, an electrically driven timer, a first circuit for applyinga predetermined voltage to the heating element including a normally openselfdocking type relay, a normally open second circuit including saidheating element, means operative when the second circuit is closed andthe resistance of the heating element departs from a predetermined valuefor energizing the relay, means operated by the timer for periodicallyclosing the second circuit, and means operated by the timer forperiodically unlocking the said relay.

3. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, an electric heating element inblanket whose resistance changes in relationship to its temperature, anelectrically driven timer, means including a normally open self-lockingtype relay for applying a predetermined voltage to the heating element,a normally open bridge circuit including said heating element, meansoperated by the timer for periodically closing said bridge circuit,means responsive to unbalance of said bridge circuit when the bridgecircult is closed for energizing the relay, and means operated by thetimer for periodically unlocking said relay.

i. A heat control arrangement for an. electrically heated blanketcomprising, in combination, a blanket, an electric heating element insaid blanket whose resistance changes in relationship to itstemperature, an electrically driven timer, a first circuit for applyinga predetermined voltage to the heating element including a normally openself-locking type relay, a second circuit ineluding said heating elementand a normally open switch, means operative when the switch is closedand the resistance of heating element departs from a predetermined valuefor r ener izing the relay, means operated by the timer for periodicallyunlocking the said relay, and means operated by the timer formomentarily closing the said switch after the relay is unlocked.

5. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, an electric heating element insaid blanket whose resistance changes in relationship to itstemperature, a first circuit including a normally open self-locking typerelay for applying a predetermined voltage to the heating element, meansincluding a normally open second circuit containing the heating element'for energizing the relay when the second circuit is closed and theresistance of the heating element departs from a predetermined value,time indicating means having a constant speed electric motor for drivingsame, and means including a switch operated periodically by said motorfor momentarily opening the first circuit to unlock the relay andmomentarily closing the second circuit in sequence.

6. A heat control arrangement for an electrically heated blanketcomprising, in combination,

a blanket, a heating element in said blanket whose resistance changes inrelationship to its temperature, a resistor subject to ambienttemperature whose resistance changes in relationship to its temperature,a bridge circuit including said heating element and resistor fordeveloping a voltage which varies in relationship to changes in thecombined resistances of said heating element and resistor, electronictube means arranged to conduct current responsive to changes in saiddeveloped voltage, a circuit for applying substantially full linevoltage to the heating element from a source of electric power, anormally open self-locking relay energized by the flow or currentthrough the tube means for closing the last named circuit, a timer, andmeans actuated periodically by the timer for opening the last namedcircuit and closing the bridge circuit in sequence.

"7. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, a heating element in said blanketwhose resistance changes in relationship to its temperature, a resistorsubject to ambient temperature whose resistance changes in relationshipto its temperature, a bridge circuit connected to a source of electricpower and including said heating element and resistor adapted whenclosed to develop a voltage which varies in relationship to changes inthe combined resistances of said heating element and resistor,electronic tube means arranged to conduct current responsive to changesin said developed voltage, a circuit for impressing a higher potentialon the heating element from the source of electric power, meansenergized by the flow of current through the tube means for closing thelast named circuit, unlockable means for retaining said last namedcircuit in closed condition, a timer, and means operated periodically bythe timer for momentarily closing the bridge circuit and then unlockingsaid retainin means after a predetermined heating period.

8. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, a heating element in said blanketwhose resistance changes in relationship to its temperature, a resistorsubject to ambient temperature whose resistance changes in relationshipto its temperature, a bridge circuit connected to a source of electricpower and including a normally openswitch adapted to establish thebridge circuit when closed, said bridge circuit including said heatingelement and said resistor and being arranged to develop a, voltage whenthe switch is closed which varies in relationship to changes in thecombined resistances of said heating element and resistor, acircuit forapplysubstantially full line voltage to the heating element from thesource of electric power and short circuiting the switch and resistorsubject to ambient temperature including a normally open self-lockingrelay, means including a second circuit for energizing the relayresponsive to the developed bridge voltage, a timer, and means operatedby the timer for unlocking the relay and momentarily closing the bridgecircuit switch in sequence. I

9. Aheat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, a heating element in said blanketwhose resistance changes in relationship ,to its temperature, a resistorsubject to ambient temperaturewhose resistance changes in relationshipto its temperature, a bridge circuit connected to a source of electricpower and including said heating element and resistor for developing avoltage which varies in relationship to changes in the combinedresistances of said heating element and resistor, an electronic tubehaving a grid voltage determined by the bridge voltage, means includinga circuit for applying substantially full line voltage to the heatingelement from the source of electric power, a normally open relayconnected to the tube and arranged to close the heating element circuitwhen the grid voltage on the tube reaches a predetermined value and tolock in closed position, actuatable means ior unlocking the relay, anormally open switch adapted to be actuated to close the bridge circuit,and a timer for periodically and momentarily actuating the unlockingmeans and the bridge circuit closing switch in sequence.

10. A heat control arrangement for an electrically heated blanketcomprising, in combination,

a blanket, a heating element in said blanket whose resistance changes inrelationship to its temperature, a resistor subject to ambienttemperature whose resistance changes in relationship to its temperature,a normally open bridge circuit connected to a source of electric powerand having one leg comprising the said heating element and resistor fordeveloping a voltage varying in relationship to changes in theresistances of said heating element and resistor, an electronic tubehaving a, grid voltage determined by the bridge voltage and arranged toconduct current when the combined resistance of said heating element andresistor fall below a predetermined minimum, a circuit for applyingsubstantially full line voltage to the heating element from the sourceof electric power including 9. normally Open relay actuated by the flowof current through the tube and adapted to lock in closed position untilthe last named circuit is opened, a timer including time indicatingmeans, and a pair of switches operated sequentially and periodically bythe timer for momentaril opening the last named circuit and closing thebridge circuit in sequence.

11. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, a heating element in said blanketwhose resistance changes in relationship to its temperature, a resistorsubject to ambient temperature whose resistance changes in relationshipto its temperature, a bridge circuit having one leg comprising the saidheating element and resistor for developing a voltage varying inrelationship to changes in the combined resistance of said heatingelement and resistor, said bridge circuit being connected to a source ofelectric power and including a normally open first switch adapted to beactuated to close the bridge circuit, an electronic tube having a gridvoltage dependent upon said developed voltage, a solenoid connected tothe tube to be energized when the grid voltage on the tube reaches avalue indicating a predetermined drop in temperature of the heatingelement and resistor, means including a circuit for applyingsubstantially full line voltage to the heating element from the sourceof electric power including a normally open switch adapted to be closedwhile the solenoid is energized, a second switch operated by thesolenoid when the solenoid is energized through the tube to disconnectthe tube from the solenoid and to connect the solenoid to a source ofelectric power, 3, normally closed switch adapted to be actuated todisconnect the solenoid from the source of electric power, and a timerconstructed and arranged to momentarily and periodically actuate saidlast named and first named switches in sequence.

ARNOLD E, RUDAHL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 915,974 Leonard Mar. 23, 19091,183,814 Haagn May 16, 1916 1,437,005 Newsom Nov. 28, 1922 1,694,264Hull Dec. 4, 1928 1,826,477 Olpp Oct. 6, 1931 2,149,542 Peltz Mar. 7,1939 2,195,958 Kearsley Apr. 2, 1940 2,429,453 Crowley Oct. 21, 19472,439,842 Clark Apr. 20, 1948 FOREIGN PATENTS Number Country Date144,669 Great Britain Sept. 9, 1921 338,880 Great Britain Nov. 18, 1930623,503 Germany Dec. 24, 1935

